fix skipping of physical checks when file does not end in newline

[asottile]

Resolves #960

[sigmavirus24]

We may need to replicate some of this logic to Flake8

[asottile]

indeed, I plan to work on that today!

[asottile]

here's the flake8 patch with essentially the same logic!

https://gitlab.com/pycqa/flake8/-/merge_requests/451

[jaraco]

Confirmed it works for the reported case (which is my actual use-case):

draft $ python -c "import pathlib; pathlib.Path('tabbed.py').write_text('def foo():\\n\\tpass')"
draft $ pip-run -q --use-pep517 git+https://github.com/asottile/pycodestyle@physical_checks_last_line -- -m pycodestyle tabbed.py
flake8 3.7.9 requires pycodestyle<2.6.0,>=2.5.0, but you'll have pycodestyle 2.6.0 which is incompatible.
tabbed.py:2:1: W191 indentation contains tabs
tabbed.py:2:6: W292 no newline at end of file